26 ESSENTIALS OF BOTANY 
kept in too moist an atmosphere, or very few root-hairs 
will be formed. Examine with the magnifying glass 
those parts of the root which have these appendages. 
Try to find out whether all the portions of the root are 
equally covered with hairs, and, if not, where they are 
most abundant (see also Fig. 10). 
The root-hairs in plants growing under ordinary condi- 
tions are surrounded by the moist soil and wrap them- 
selves around microscopical particles of earth (Fig. 11). 
Thus they are able to absorb rapidly through their thin 
walls the soil-water with whatever mineral substances it 
has dissolved in it. 
35. The Young Stem. — The hypocotyl, or portion of 
the stem which lies below the cotyledons, is the earliest 
formed portion of the stem. Sometimes this lengthens but 
little, as in Fig. 2; often, however, as the student knows 
from his own observations, the hypocotyl lengthens enough 
to raise the cotyledons well above ground, as in Fig. 9. 
The later portions of the stem are considered to be 
divided into successive nodes (places at which a leaf, or 
a scale which represents a leaf, appears) and internodes 
(portions between the leaves). 
The student should watch the growth of a seedling bean 
or pea and ascertain by actual measurements whether the 
internodes lengthen after they have once been formed, and, 
if so, for how long a time the increase continues. 
36. The First Leaves. — The cotyledons are, as already 
explained, the first leaves which the seedling possesses, — 
even if a plumule is found well developed in the seed, it 
was formed after the cotyledons. In those plants which 
have so much food stored in the cotyledons as to render 
these unfit ever to become useful foliage leaves, there is 
